Experimental Tests of the New Paradigm for Laser Filamentation in Gases

Since their discovery in the mid-1990s, ultrafast laser filaments in gases have been described as products of a dynamic balance between Kerr self-focusing and defocusing by free electric charges that are generated via multi-photon ionization on the beam axis. This established paradigm has been recently challenged by a suggestion that the Kerr effect saturates and even changes sign at high intensity of light, and that this sign reversal, not free-charge defocusing, is the dominant mechanism responsible for the extended propagation of laser filaments. We report qualitative tests of the new theory based on electrical and optical measurements of plasma density in femtosecond laser filaments in air and argon. Our results consistently support the established paradigm.Comment: 4 pages, 4 figure

X-ray structural studies of lanthanide macrocycles and biological molecules

The work described in this thesis is broadly divided into two sections. The structural study on the lanthanide macrocyclic complexes was afforded by means of X-ray crystallography In this chapter, the molecules dota, the cationic enantiopure tetraamide europium and dysprosium complexes, the sodium complexes of the tetranaphthylamide and quinoyl derivative, the enantiopure gadolinium and europium complexes of the tetraamide series with esteratic sidechains, the lanathanum and ytterbium complexes of the dota derivative with benzyl phosphinate sidechains, and the tetracarboxyethyl series both as three uncomplexed stereoisomer and complexes of the RRRR stereoisomer with europium, gadolinium and terbium. These complexes exhibit quite a lot of structural diversity. Chapter five deals with experiments carried out at ultra low temperatures. A phase transition that the molecule benzil undergoes is investigated on the Fddd diffractometer, a study of the interesting 1,12-dicarbonyl borane was undertaken to obtain precise values for the carbonyl bond lengths and the unprecedented structure of its hydrate was revealed to be a carbene diol and not the expected carboxylic acid complex The standard for macromolecular tests for diffraction, chicken egg white lysozyme, was crystallised and used to optimise conditions for low-temperature data acquisition from macromolecular samples The work described in this Thesis was carried out in the Department of Chemistry, Durham University from October 1995 to January 1999, under the supervision of Professor J.A.K. Howard. All of the work is my own, unless stated to the contrary, and it has not been submitted previously for a degree at this or any other university

SELF-FORGIVENESS IN ROMANTIC RELATIONSHIPS: THE IMPACT ON THE PERPETRATOR AND THE RELATIONSHIP

Two studies were conducted to determine how self-forgiveness and other perpetrator reactions influence the perpetrator and the victim after a romantic relationship transgression. Study 1 used a longitudinal design to determine how guilt and shame predicted the trajectory of self-forgiveness, self-excusing, and self-punishing in participants who had recently been the perpetrator of a romantic relationship transgression. Those experiencing higher guilt at baseline had higher self-forgiveness starting out and those lower on guilt starting out had a greater change in self-forgiveness. Those experiencing more guilt at baseline experienced less change in self-forgiveness over time. Shame was not significantly related to self-forgiveness over time. Those experiencing higher shame at baseline were higher in self-excusing starting out. Those lower on shame starting out had a greater increase in self-excusing over time and those experiencing more shame at baseline experienced less increase in self-excusing over time. Guilt was not significantly related to self-excusing over time. Neither guilt nor shame predicted change in self-punishment over time. In Study 2, couples came into the lab and wrote about the same offense. One participant wrote from the perspective of the perpetrator and the other from the perspective of the victim. Victims reported their forgiveness and perception of their partners’ reactions to wrongdoing. Perpetrators reported their perception of their partners’ feelings of forgiveness and their feelings of self-forgiveness, self-excusing, and self-punishing. Both members reported their relationship satisfaction and commitment. Overall, self-forgiveness by the perpetrator was not a strong predictor of perpetrator satisfaction or commitment. Victims were more satisfied and committed when perceiving self-forgiveness from their partner, even though their partners’ self-forgiveness did not have an effect. Self-forgiveness only positively predicted perpetrators’ satisfaction and commitment when participants reported decisional self-forgiveness. Victims’ perceptions of the perpetrators’ self-excusing and perpetrators’ self-punishing negatively predicted victim commitment and satisfaction. Victims’ perceived perpetrator self-punishing positively predicted perpetrators’ commitment. Perpetrator perceived victim forgiveness and victim forgiveness both positively predicted satisfaction for the perpetrator and the victim. This suggests that perpetrators’ perceptions of victim forgiveness may be more important for the perpetrator than the victim actually forgiving them

Nutritive value of forage legumes used for grazing and silage

peer-reviewedLegume forages have an important position in ruminant production in Western Europe and with further development can play an even larger role. Red clover for silage and white clover in grazed swards lead to enhanced growth rate and milk yield in comparison with pure grasses. Much of the production benefit of these legumes relates to enhanced intake since digestibilities are not markedly different to grasses. The higher intake of legume silages reflects differences in the cell structure of legume plants which combined with high fermentation rates means that they break down into small particles in the rumen, and leave the rumen more rapidly than perennial ryegrass. Ease of ingestion leads to high rates of intake, which explains higher intakes for grazed legumes. A further benefit of legumes is the reduced rate of decline in digestibility with advancing maturity. Whilst legumes have limited effects on gross milk composition or carcass characteristics, there are marked increases in levels of beneficial n−3 PUFA. Legumes have often led to a reduction in methane production from the rumen and again, this relates to both physical and chemical differences between forage species. The high rates of release of soluble protein and of breakdown to small particles from clovers and lucerne is associated with susceptibility to bloat, which is a limitation to further exploitation in grazing systems. The high concentration of rapidly degraded protein in legumes also leads to inefficient utilisation of dietary N and increased urinary N output. Research with tanniniferous forages, such as birdsfoot trefoil and sulla, demonstrates the potential for future legumes with reduced environmental and health effects, though these particular forage legumes are not well adapted to temperate regions of Western Europe that are the focus of this review

An examination of the molecular mechanisms controlling the tissue accumulation of conjugated linoleic acid (CLA) in cattle

End of project reportLong chain n-3 polyunsaturated fatty acids (n-3 PUFA) and conjugated linoleic acid (CLA) have demonstrable and potential human health benefits in terms of preventing cancer, diabetes, chronic inflammation, obesity and coronary heart disease. Supplementation of cattle diets with a blend of oils rich in n-3 PUFA and linoleic acid have a synergistic effect on the accumulation of ruminal and tissue concentrations of trans vaccenic acid (TVA), the main substrate for ?-9 desaturase which is responsible for de novo tissue synthesis of the cis 9, trans 11 isomer of CLA. This dietary strategy translates into increases in milk concentrations of CLA in dairy cows; however, concentrations in the muscle of beef animals have not always been increased. There is an apparent paradox in that n-3 PUFA supplementation enhances ruminal synthesis of trans-vaccenic acid (TVA), but then inhibits its conversion to CLA possibly through altering the activity of ?-9 desaturase. Recently, the promoter regions of the bovine ?- 9 desaturase gene has been isolated and analysed and has been shown to contain a conserved PUFA response region

Analogue Gravity and ultrashort laser pulse filamentation

Ultrashort laser pulse filaments in dispersive nonlinear Kerr media induce a moving refractive index perturbation which modifies the space-time geometry as seen by co-propagating light rays. We study the analogue geometry induced by the filament and show that one of the most evident features of filamentation, namely conical emission, may be precisely reconstructed from the geodesics. We highlight the existence of favorable conditions for the study of analogue black hole kinematics and Hawking type radiation.Comment: 4 pages, revised versio

Origin of the approximate universality of distributions in equilibrium correlated systems

We propose an interpretation of previous experimental and numerical experiments, showing that for a large class of systems, distributions of global quantities are similar to a distribution originally obtained for the magnetization in the 2D-XY model . This approach, developed for the Ising model, is based on previous numerical observations. We obtain an effective action using a perturbative method, which successfully describes the order parameter fluctuations near the phase transition. This leads to a direct link between the D-dimensional Ising model and the XY model in the same dimension, which appears to be a generic feature of many equilibrium critical systems and which is at the heart of the above observations.Comment: To appear in Europhysics Letter